Device for muscle stimulation

ABSTRACT

The invention relates to a device for muscle stimulation, said device comprising a pulse generator unit ( 9 ) for producing and sending an electrical stimulation pulse; a control unit ( 10 ) for controlling the pulse generator unit ( 9 ) in order to adjust the amplitude and the frequency of the stimulation pulses and to cause the transmission of stimulation pulses to a muscle to be stimulated; a detection unit ( 11 ) for detecting the instantaneous, spontaneous or stimulated cardiac rhythm of the carrier of the device; a housing ( 12 ) receiving the pulse generator unit ( 9 ), the control unit ( 10 ), and the detection unit ( 11 ); a counting unit ( 13 ) and a memory unit ( 14 ) for counting and storing the number of stimulation pulses emitted within a definable time interval; and a determination unit ( 15 ) for determining the arithmetic average of the stimulation frequency within the definable time interval.

BACKGROUND OF THE INVENTION

The invention relates to a device for muscle stimulation.

Muscle-driven heart assist systems (for example cardio myoplasty, aortamyoplasty, skeletal muscle ventricle, bio-mechanical hearts) arenowadays already employed in clinical settings, for exampleexperimentally as assist or replacement therapy of heart transplantationand treatment of a terminal heart insufficiency. These muscle assistsystems can operate both in parallel and in series with the diseasedheart. The systems are intended to relieve (reduce the cardiac walltension, relieve pressure, relieve volume, relieve post-stress) and alsoto assist the circulation, i.e., increase the average pressure of thearterial blood pressure and/or to increase the pump volume. Independentof the configuration of the heart assist system, a muscle pacemaker isrequired for deliberate stimulation of a muscle contraction, whichtransmits to the muscle to be assisted an electrical stimulation patternin synchronism with the heart beat via stimulation electrodes. Astimulation pattern consists of a sum of individual pulses which can becharacterized by their stimulation voltage, the pulse width and thespacing between two pulses. By a meaningful combination of severalindividual pulses to a group of individual pulses with a subsequentpause, a stimulation burst is created which can be used cyclicallycontract and relax the muscle tissue. In addition to the aforedescribedparameters, the number of stimulation pulses per burst and the frequencywith which a stimulation burst is applied can be used to describe astimulation pattern. An additional parameter is the placement of thestimulation burst within the heart cycle, which can be defined by adelay time.

Experiments on large animals have shown that a continuous and frequentapplication of stimulation burst causes a fiber transformation of thestimulated muscle tissue, with the generated muscle fibers beingsubstantially free of fatigue, but weak and slow. It has been observedthat the muscle fiber cross-sections significantly decrease whenstimulation bursts are applied continuously and frequently. The muscletissue, which is here mainly represented by the type-I muscle fibers, isbarely suitable to perform the pumping benefiting the circulation.However, experimental tests have shown that before the stimulated musclefibers are transformed into type-I muscle fibers, they are transformedinto an intermediate, already fatigue-free form, which still includesstrong type-IIa muscle fibers. This quick and strong muscle tissue,which is dominated by type-IIa muscle fibers, is only preserved if thenumber of applied stimulation pulses per time interval remains below anupper limit value. Stimulation above this upper limit causes thetype-IIa muscle fibers to transformation into type-I muscle fibers,accompanied by a loss in muscle strength and quickness.

Conventional muscle pacemaker systems are capable of supplyingpredefined or computed stimulation bursts synchronously with andtriggered by the heart rhythm, wherein the ratio of muscle contractionto heart contraction is adjustable. This ratio can be predefined as afunction of the heart rate. For example, if a high heart rate persistsover an extended period of time, then the same high number ofstimulation pulses is supplied by the muscle pacemaker. The utilizationof the muscular heart assist system is then exceedingly high, so thatmost of the muscle fibers are transformed into weak and slow type-Imuscle fibers. Muscular-driven heart assist systems then lose theireffectiveness, so that the diseased heart can no longer be effectivelyrelieved. The support of the circulatory system deteriorates withincreased utilization, so that the heart rate of the patient mayincrease further to compensate this effect. This can cause the supportedmuscle to completely degenerate.

DE 101 52 741 A1 discloses a heart therapy device, in particular animplantable defibrillator, heart pacemaker or combined heartpacemaker-defibrillator, with an evaluation and control unit forevaluating a measured heart rate. The evaluation and control unitincludes a memory with three ranges for storing a first, a second, and athird range of values of comparative heart rates. The adjacent rangesare organized by increasing values of the heart rate. The evaluation andcontrol unit further includes a heart rate discriminator for associatinga measured heart rate with the first, second or third range of values,and a stability evaluation unit for evaluating the stability orconstancy of the heart rate over a predetermined time interval, when aheart rate in the second range of values is detected. When a heart ratein the second range of values is detected, one of two different therapycontrol signals is supplied, depending on the stability of the heartrate. The stability criterion is used to distinguish between “rapid”tachycardia (“flutter”) and fibrillations with a-still-relatively lowfrequency. U.S. Pat. No. 4,406,287 also discloses a pacemaker. Thisdevice is intended to terminate tachycardia, wherein different pulsenumbers/pulse rates can be employed. If tachycardia is not terminatedafter applying a first combination of a certain number of pulses and acertain pulse rate, then a second phase is applied with a changedcombination of pulse number and pulse rate. The last successfulcombination of pulse number and pulse rate is then stored as a startingvalue for terminating the next tachycardia. With this approach, theprobability for terminating a tachycardia can be enhanced.

U.S. published patent application 2003/0083703 A1 discloses a method anda device for providing an anti-tachycardia pulse pattern. This device isalso capable of determining if a pulse pattern has terminated atachycardia and if a change in the pulse pattern is indicated.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a musclestimulator which makes it possible to preserve type-IIa muscle fibersand, more particularly, to provide an effective heart muscle assistsystem which operates when needed. The muscle stimulator should also becapable of inducing, through suitable electrical stimulation, theformation of new blood vessels and capillaries for optimally supplyingthe muscle tissue with blood (neo-vascularization).

The object can be solved with a muscle stimulator which includes a pulsegenerator unit for generating and transmitting an electric stimulationpulse, a control unit for controlling the pulse generator unit (9) forsetting amplitude and frequency of the stimulation pulses and forcausing stimulation pulses to be applied to a muscle to be stimulated, adetection unit for detecting the instantaneous, spontaneous orstimulated heart rhythm of the wearer of the device, a housing forreceiving the pulse generator unit, the control unit and the detectionunit, wherein a counting unit and a memory unit for counting and storingthe number of stimulation pulses transmitted during a defined timeinterval, and a determination unit for determining an arithmeticallyaveraged (mean) stimulation frequency within the definable time intervalare provided, wherein the mean stimulation frequency is computed as thequotient of the stimulation pulses transmitted during the defined timeinterval and stored in the memory unit and the defined time interval inwhich the stimulation pulses are counted and stored.

The subject matter of the present invention is directed to a musclestimulator with a pulse generator unit for producing and transmitting anelectrical stimulation pulse, as well as a control unit for controllingthe pulse generator unit. The amplitude, i.e., the stimulation voltage,the frequency, the temporal distribution of the stimulation pulses, thetype and frequency of the support modes and the delay time relative tothe R-spike, the day/night rhythm and the phase position of thestimulation pulse can be adjusted with the control unit. The stimulationpulses are transmitted from the control unit via wiring means to one ormore muscles to be stimulated. The muscle stimulator according to theinvention also includes a determination unit for determining theinstantaneous, spontaneous or the stimulated heart rhythm of the wearerof the muscle stimulator. The determination unit measures the R-spike,which is used as a basis for triggering the stimulation pulse and forcalculating the time delay between the R-spike of the heart rhythm andthe stimulation burst. The pulse generator unit, the control unit, andthe detection unit are housed in a common housing, which can be carriedexternal to the patient's body or can be implanted in the patient'sbody.

A counting unit and a memory unit for counting and storing the number ofstimulation pulses transmitted within a definable time interval are alsoprovided, as is a determination unit for determining a mean stimulationfrequency within the definable time interval.

The mean stimulation frequency according to the invention is thequotient formed of the stimulation pulses, which are supplied within adefinable time interval and stored by the memory unit, and the definedtime interval, during which the stimulation pulses are counted andstored (detection time interval/observation time interval). Thisrepresents an arithmetically averaged (mean) stimulation frequency,whereby in the following the term “mean stimulation frequency” will beused interchangeably with “arithmetically averaged stimulationfrequency.”

The counting unit and/or the memory unit and/or the determination unitare not necessarily housed inside the aforementioned housing, but mayalso be housed in a separate housing, in particular a housing carriedexternal to the patient's body.

To prevent the stimulated muscles from being overstimulated and thestimulated muscle fibers from being transformed into a weak, slow andhence ineffective type-I muscle tissue, the stimulation pulsestransmitted within a definable time interval must be counted andevaluated. This task is performed by the counting unit in cooperationwith the storage unit and a monitoring unit. The mean stimulationfrequency is a measure for the frequency with which the muscles arestimulated during a certain time interval. To prevent muscle damage, themean stimulation frequency must not continuously exceed an individuallydetermined limit value.

Each transmitted stimulation pulse is counted and computed over anextended observation time to yield a mean stimulation frequency. Alonger observation time according to the invention has a duration of atleast 30 minutes, in particular one hour or several hours.Advantageously, observation times are 12 or 24 hours. The meanstimulation frequency must be determined individually for each patientand must not exceed a maximum value of the 0.2 to 2 pulses per second(Hz), in particular 0.7 to 1 Hz, so as to prevent overexertion of themuscle and a medium-term muscle destruction. The mean stimulationfrequency should therefore be evaluated so as to arrive at the desiredmuscle transformation and preservation effect, and to control thetransmission of stimulation pulses depending on the outcome of theevaluation. For this purpose, a continuously operating evaluation unitfor observing the limit values for the mean stimulation frequency isprovided, wherein the limit values can be individually set in a range of0.2 stimulation pulses per second to 2 stimulation pulses per second.Pulse conservation means, also referred to as pulse saving means, areprovided for adapting and, more particularly, reducing the meanstimulation frequency as a function of the measured mean stimulationfrequency and the defined desired values of the evaluation unit. Thepulse conservation means include a computing unit for computing amodified stimulation pattern according to an equation which depends onthe mean stimulation frequency. In addition, a memory module for storingthe temporal course of the number of supplied stimulation pulses can beprovided, as well as means for program-controlled transmission of themean stimulation frequency from the determination unit to the computingunit. Moreover, an analysis unit can be provided for determining whenand how often certain limit values of the heart rate and/or of the meanstimulation frequency are exceeded or underrun.

The counting unit and the memory unit can be housed in theaforedescribed housing. The determination unit and/or the pulseconservation means can also be integrated in the housing. Optionally,the memory module and/or the analysis unit can also be integrated in thehousing that houses the control unit. The housing can be implanted inthe body of the wearer of the device of the invention. An energy storagedevice which can preferably be recharged transcutaneously can also beassociated with the housing. This increases the operating time of theimplanted part of the device.

Within the context of the invention, the counting unit and/or the memoryunit and/or the determination unit and/or the pulse conservation meansand/or the memory module and/or the analysis unit can form a part of astationary monitoring unit and/or a monitoring unit worn by the wearerof the device external to the body. The mean stimulation frequencyand/or a range of values in which the mean stimulation frequency falls,can be optically and/or acoustically and/or haptically displayed on themonitoring unit. The monitoring unit can optionally include programmingunit for generating a programming signal and a transmission unit fortransmitting the programming signal to a send and receive unit in thehousing which houses the control unit. The monitoring unit can alsoinclude means for sending and receiving position data. The monitoringunit can further includes means for sending and receiving wirelesssignals for the purpose of transmitting patient-physiological data to adisplay and evaluation unit of a receiver

It is another object of the invention to provide a combination ofspecially developed electronic devices for muscular heart assistsystems, in particular for muscular blood pumps, capable of generatingand maintaining type-IIa muscle fibers. The invention also relates to amyo-stimulator which can be programmed to preoperatively generatethrough percutaneous stimulation type-IIa muscle fibers showing lessfatigue. This device can include an implantable myo-stimulator and amonitoring unit which effectively contracts the muscle with type-IIamuscle fibers, prevents conversion to type-I muscle fibers, and alsoprevents destruction of muscle from excessive stress. The monitoringunit associated with this implantable myo-stimulator can be used as aprogramming unit as well as a measurement and display device. Themonitoring unit can transmit information either wireless or by a wiredconnection from the bio-stimulator to the patient or to the attendingphysician. Additional functions can be incorporated in this device, suchas transmitting the ECG of the patient and/or a patient location systemfor emergencies. This device can also implement to a limited extent theaforedescribed functions in myo-stimulators of other manufacturers.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described with reference to schematicallyillustrated embodiments.

FIG. 1 shows schematically the interconnections between differentphysical elements of an apparatus of the invention;

FIG. 2 is a diagram of the functional elements of a first embodiment ofa device for muscle stimulation;

FIG. 3 shows a modification of the embodiment of FIG. 1; and

FIG. 4 shows another variation of the device for muscle stimulation withadditional functional elements.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 depicts an embodiment with two microcontrollers 1, 2 asprogrammable components. The microcontrollers have a large number ofprogrammable ports, a high processing speed with moderate powerconsumption, and a flash memory with in-system programmability (ISP).Additional components of the muscle pacemaker are a 12 bitanalog-to-digital converter (A/D converter) 3, a 12 bitdigital-to-analog converter (D/A converter) 4, several operationalamplifiers, and a telemetry unit 5. Long-life batteries, preferablylithium ion batteries, supply power.

The digital portion of the muscle pacemaker is essentially divided intotwo logically separate regions, which are each operated with a dedicatedmicrocontroller 1, 2 as programmable components. The first region,controlled by the microcontrollers 1, is used to generate, amplify anddistribute the stimulation pulses S (max. 40 mA) to four muscleelectrodes and two cardiac electrodes. The second region, controlled bythe microcontroller 2, is used for monitoring the patient, for capturingand storing measurement data, e.g., pressure data D, which are processedin a pressure logic 6 and then supplied to the microcontroller 2 whichoperates as a measurement unit, as well as for telemetric communicationwith the environment. The two logical regions are connected with eachother via a multi-purpose connection in the form of a serial interface7. The two microcontrollers 1, 2 are programmed, for example, in theprogramming language “C”. The actual software of the microcontrollers 1,2 can be different, depending on their specific function.

The functions of the aforementioned logically separate regions will nowbe described in more detail.

Region 1:

Triggering From the Heart Action:

To suitably place a stimulation pulse within a heart cycle, themicrocontroller 1 receives synchronously with each heart action atrigger signal from a filter circuit (R-spike unit) 8, which includes 8cascaded operational amplifiers OPV. The first four OPVs amplify thereceives ECG signal from approximately 1-10 mV to 2-3 V and filter outinterference frequencies of 50 Hz and 60 Hz. The additional 4 stages areused to extract the R-spike and to generate a Schmitt-trigger signal.This trigger signal is detected by the microcontroller 1, and the timeinterval from the preceding trigger signal is determined. If thedetermined time interval is normal when compared to the last 10 triggerintervals, a stable sinusoidal rhythm of the heart is assumed and theheart rate is determined from the spacing of the trigger signals R. Eachof the arrows having the reference symbol P indicates serial high-speedlinks.

Assist Modes

Different ratios of the muscle contraction to heart contraction aredesirable depending on the heart rate. The adjustable range is between1:1, i.e., each heart action is supported by a muscle action, and 1:255,i.e., the muscle contracts only after 255 heart actions. Up to 5different support modes can be defined depending on the heart rate.

Day-Night Rhythm and/or Activity-Rest Rhythm

Day times and night times and, independently thereof, activity times andrest times can be defined for the muscle pacemaker, whereby the musclepacemaker switches between pulse patterns having high activity and pulsepatterns having low activity or no activity. The switch between day andnight rhythms and/or activity-rest rhythms can be time-dependent,event-controlled, or manually through a controller of the patient.

Time Sequence Before a Muscle Stimulation

When a heart trigger signal R is received and the signal is deemed to beregular, a counter performs an addition until a heart pulse occurs whichrequires assistance. Thereafter, a second counter is activated whichintroduces a certain time delay before the stimulation pattern isgenerated (R-spike delay, R-delay).

Time Sequence During a Muscle Stimulation

At the end of the R-spike delay time (R-delay), the D/A converter 4 andan operational amplifier circuit (OPV) generate the stimulation patternpulse-by-pulse, depending on the preset, with the variables: amplitude,pulse width, pulse phase (positive, negative, biphasic) and inter-pulsespacing, and supply the stimulation pattern to defined stimulationelectrodes.

Quantifying the Stimulation Pulse

Each supplied stimulation pulse is counted and a mean stimulationfrequency is computed over an observation time interval of, for example,24 hours. The mean stimulation frequency must be determined individuallyfor each patient and must not exceed a maximum value of approximately0.2 Hz to 2 Hz, in particular 0.7 to 1 Hz, so as to preventoverstraining the muscle and medium-term muscle destruction.

Output of the Mean Stimulation Frequency

Providing an output of the mean stimulation frequency represents animportant and novel feedback mechanisms for the wearer of the musclepacemaker and for the attending physician, so that overstraining themuscle can be identified early and countermeasures can be taken toprevent potential destruction of the muscle. The microcontrollertransmits the mean stimulation frequency via a radio link in regularintervals, which can be adjusted by the physician, which is received bya portable patient monitor and is indicated to the patient, for example,displayed. If the mean stimulation frequency is in a critical range, themicrocontroller transmits the data immediately; the patient monitor thensignals an overload alert. The patient can then reduce the heart rateand the frequency of assist of the heart muscle by reducing his/herbodily activity.

Pulse Conservation Mode

If the mean stimulation frequency is in a range close to the upperlimit, then the automatic pulse conservation mode can be operative, ifthis mode was activated by the physician and/or by the wearer of theimplant. In this mode, the stimulation pulses are distributed within thestimulation burst at a low activity, so that initially a sufficientnumber of pulses for a muscle contraction is generated, whereas duringthe further course of the stimulation one to two pulses are cut out bystretching, i.e., reducing the stimulation frequency. For safetyreasons, this mechanism is not operative in phases of high activity.

Region 2:

Patient Monitoring and Communication Unit

The second region of the muscle pacemaker is used for monitoring thepatient, for measuring and storing the measurement data, and fortelemetric communication with the environment.

Real-Time Patient Monitoring

Real-time patient monitoring allows the attending physician to gain anoverview over the instantaneous physiological data, such as ECG, EMG,and blood pressure. After activation of the measurement module, the datafrom the implanted device are measured via the respective electrodes(ECG and heart rhythm; heart sensing electrodes; EMG: stimulationelectrodes) and sensors (absolute pressure sensor), digitized andtransmitted in compressed form to the outside via a radio link. The dataare graphically displayed on the receiving monitoring unit (patientmonitor) and logged. The patient monitor can include an interface with atelecommunication path, for example a telephone line, for remotediagnostic monitoring of the patient.

Measuring and Storing of “Long-Term” Physiological Data

The monitoring unit of the muscle pacemaker measures cyclically(adjustable from 1 minute to 1 hour) the heart rate and the systolic anddiastolic blood pressure. These data are stored internally in thepacemaker in form of a table, and a trend analysis is performed. Thisstored table values are transferred routinely, once a day, to themonitoring unit which transmits the data to the attending physician, forexample via a telephone dial-up connection. However, if the trendanalysis indicates a life-threatening risk for the patient, then theresult of the analysis is immediately telemetrically transferred to themonitoring unit. If limit values defined by the physician are exceeded,then the monitoring unit informs the attending physician or an emergencycenter and transmits, in particular, via a wireless radio link(UMTS/GSM) both the patient data and the GPS position of the patient.

Programmability of the Muscle Pacemaker

The implanted device must be capable of responding to external inquiriesfor changing the existing stimulation pattern and foractivating/deactivating the various operating modes. For this reason,the telemetry component and the microcontroller 2 are periodicallyplaced in a receive mode (adjustable from seconds to several hours).

The following parameters of the stimulation pattern can be reprogrammed:

-   -   Stimulation voltage,    -   Stimulation phase,    -   Temporal distribution of the stimulation pulses,    -   Type and frequency of the assist modes,    -   Delay time relative to the R-spike,    -   Duration of the day and night rhythm, or of the activity and        rest rhythm,    -   Electrode position.

The following operating modes can be activated and/or deactivated:

-   -   Day and night rhythm, or the activity and rest rhythm,    -   Pulse conservation mode,    -   Real-time capture of measurement data,    -   Pacemaker diagnostic program,    -   Impedance measurement of the stimulation electrodes,    -   Battery voltage measurement.

The patient monitor (monitoring unit) is a battery-operated system thatcan be worn by a patient.

It can be used for

-   -   Self-check by the patient to attain the mean stimulation        frequency in a range from 0.2 Hz to 2 Hz, in particular 0.7 to 1        Hz, over for example 24 hours, whereby an illuminated color        display (green, yellow, red) signals the mean stimulation        frequency, which is periodically updated;    -   Tele-monitoring the patient by the attending physician, wherein        the physiological real-time and long-term data measured by the        implant are telemetrically received, logged and routed onward.        The data can be routed onward either via the integrated        telephone modem or via a radio link in a wireless network, for        example a UMTS/GSM network;    -   Determining the position of the patient in emergency situations        via an integrated GPS receiver;    -   A programming unit to allow the patient him-/herself to set        fundamental stimulation parameters and operating modes.

The patient monitor includes a microcontroller, a telemetry module, astandard GPS receiver, a standard modem and a UMTS/GSM module.

The patient monitor is provided with a graphic display and illuminationmeans, in particular an LED display, for visualizing the meanstimulation frequency and status messages of the system. The data can beentered under menu-control via keys or alternatively by using a stylus.

FIG. 2 shows a device for muscle stimulation with a pulse generator unit9 for generating and sending an electric stimulation pulse, a controlunit 10 for controlling the pulse generator unit 9, for setting theamplitude and frequency of the stimulation pulses, and for causingtransmission of stimulation pulses to a muscle requiring stimulation. Adetection unit 11 for measuring the instantaneous, spontaneous, orstimulated heart rhythm of the wearer of the device is also provided.The basic components of the device of the invention for musclestimulation are housed in a common housing 12. The housing also includesa counting unit 13 and a memory unit 14 for counting and storing thenumber of stimulation pulses supplied within a definable time interval.An additional determination unit 15 is used to determine a meanstimulation frequency within a definable time interval. The housing 12also includes a pulse conservation means 16 with a computing unit 17.The computing unit 17 is used to compute a stimulation pattern accordingto an equation which determines the stimulation pattern as a function ofthe mean stimulation frequency.

Unlike the embodiment depicted in FIG. 2, the embodiment of FIG. 3includes two spatially separated housings 12, 18. The housing 12 withthe pulse generator unit 9, the control unit 10 and the detection unit11, as well as a send and receive unit 19 for communicating with thecomponent in the other housing 18, can be implanted in the patient'sbody. In the depicted exemplary embodiment, the counting unit 13, thememory unit 14, the determination unit 15 and the pulse conservationmeans 16 are spatially separate from the implanted housing. Therespective housings 12, 18 can communicate via a wireless communicationlink provided by the send and receive unit 19 and the transmissiondevice 20 in the respective housings.

The embodiment of FIG. 4 has additional components in the housing 18located external to the patient's body. The housing 18 further includesa memory module 21 for storing the temporal course of the number ofapplied stimulation pulses, and an analysis unit 22 for determining howoften and when the heart rate and/or the mean stimulation frequencyexceeded or fell below certain limit values. These components are shownin FIG. 4 with dash-dotted lines and can optionally also be includeddirectly in the implanted housing 12. A broken line in the diagram ofFIG. 4 is meant to indicate that these components are located adjacentto the housing 12. Because in the exemplary embodiment of FIG. 4 majorfunctional components of the device of the invention are arranged in thehousing 18 external to the patient's body, this assembly can alsofunction as the monitoring unit 23. A programming unit 24 is provided onthe monitoring unit 23, with programmed control commands being suppliedvia the transmission unit 20 and the send and receive unit 19 to thecontrol unit 10 in the housing 12. In the depicted exemplary embodiment,the monitoring unit 23 further includes means 25 for sending andreceiving position data, as well as means 26 for sending and receivingradio signals to transmit patient-physiological data to a display andevaluation unit of a receiver. The monitoring unit 23 includes opticaland/or acoustic and/or haptic display means for indicating the meanstimulation frequency.

1. A device for stimulating a muscle contraction of a muscular-driven heart assist system which operates in parallel or in series with a diseased heart, comprising: a pulse generator unit for generating and supplying electric stimulation pulses to a muscle of the muscular-driven heart assist system; a control unit for controlling the pulse generator unit for setting an amplitude and a frequency of the stimulation pulses and for causing the stimulation pulses to be applied to the muscle of the muscular-driven heart assist system to be stimulated; a detection unit for detecting an instantaneous, spontaneous or stimulated heart rhythm of a wearer of the device; a housing receiving the pulse generator unit, the control unit and the detection unit; a memory module for storing a temporal course of the number of supplied stimulation pulses within a defined time interval; a counting unit and a memory unit for counting and storing a number of stimulation pulses supplied during the defined time interval, wherein the stimulation pulses are grouped into variable stimulation bursts; a determination unit for determining an arithmetically averaged (mean) stimulation frequency within the defined time interval, with the mean stimulation frequency being computed as the quotient of the number of stimulation pulses of the variable stimulation bursts supplied during the defined time interval and stored in the memory unit and the defined time interval in which the stimulation pulses are counted and stored; a continuously operating evaluation unit for ascertaining that the mean stimulation frequency stays within preset limit values, wherein the limit values of the mean stimulation frequency can be preset in a range between 0.2 stimulation pulses per second and a maximum of 2 stimulation pulses per second; pulse conservation means for reducing the mean stimulation frequency depending on the limit values preset in the evaluation unit, wherein the pulse conservation means comprise a computing unit configured to compute a stimulation pattern according to an equation which determines the stimulation pattern as a function of the mean stimulation frequency and varies the number of stimulation pulses during a stimulation burst to generate and maintain type-IIa muscle fibers and to revent their conversion to type-I muscle fibers; and a monitoring unit worn by the wearer of the device external to the body for displaying the mean stimulation frequency and for self-control of the patient.
 2. The device of claim 1, further comprising means for program-controlled transmission of the mean stimulation frequency from the determination unit to the evaluation unit.
 3. The device of claim 1, further comprising an analysis unit for determining how often and when certain limit values of the heart rate and/or of the mean stimulation frequency are exceeded or underrun.
 4. The device of claim 1, wherein the counting unit and the memory unit are received in the housing.
 5. The device of claim 1, wherein the determination unit and/or the pulse conservation means are integrated in the housing which receives the control unit.
 6. The device of to claim 3, wherein the memory module and/or the analysis unit are integrated in the housing which receives the control unit.
 7. The device of claim 1, wherein the monitoring unit comprises a programming unit for generating a programming signal, and a transmission unit for transmitting the programming signal to a send and receive unit located in the housing which receives the control unit.
 8. The device of claim 1, wherein at least one of the counting unit, the memory unit, the determination unit, the pulse conservation means, the memory module and the analysis unit are a part of a stationary monitoring unit or of the monitoring unit worn by the wearer of the device external to the body.
 9. The device of claim 1, wherein the mean stimulation frequency, or an order of magnitude of the mean stimulation frequency, is displayed on the monitoring unit by optical, acoustic or haptic means, or a combination thereof.
 10. The device of claim 1, wherein the monitoring unit includes means for sending and receiving position data.
 11. The device of claim 10, wherein the monitoring unit includes means for sending and receiving wireless signals for transmitting patient-physiological data to a display and evaluation unit of a remote receiver.
 12. The device of claim 1, wherein the pulse generator unit transmits biphasic stimulation pulses.
 13. The device of claim 1, further comprising a transcutaneously chargeable energy storage device received in the housing.
 14. The device of claim 1, wherein the defined time interval is at least 30 minutes.
 15. The device of claim 1, wherein the defined time interval is at least 12 hours.
 16. The device of claim 1, wherein the defined time interval is at least 24 hours.
 17. The device of claim 1, wherein the amplitude of the stimulation pulses within a stimulation burst is variable.
 18. The device of claim 1, wherein a pulse width of the stimulation pulses within a stimulation burst is variable.
 19. The device of claim 1, wherein a temporal spacing between two stimulation pulses within a stimulation burst is variable.
 20. A method for generating and maintaining type-IIa muscle fibers and prevent their conversion to type-I muscle fibers in a muscular-driven heart assist system which operates in parallel or in series with a diseased heart, comprising the steps of: detecting an instantaneous, spontaneous or stimulated heart rhythm of the diseased heart; setting a limit value for an mean stimulation frequency for stimulation pulses applied to the heart assist system between a minimum of 0.2 stimulation pulses per second and a maximum of 2 stimulation pulses per second; setting a pattern of the stimulation pulses based on the heart rhythm, with the stimulation pulses being grouped into variable stimulation bursts; determining the mean stimulation frequency from a total number of applied stimulation pulses during a defined time interval; and if the mean stimulation frequency exceeds the upper limit value, decreasing the number of the stimulation pulses in the stimulation bursts so as to reduce the mean stimulation frequency below the limit value and to generate and maintain the type-IIa muscle fibers.
 21. The method of claim 20, wherein the limit value is between a minimum of 0.7 stimulation pulses per second and a maximum of 1 stimulation pulse per second.
 22. The method of claim 20, wherein the defined time interval is at least 1 hour.
 23. The method of claim 20, wherein the defined time interval is between 12 hours and 24 hours.
 24. The method of claim 20, and further displaying the mean stimulation frequency and displaying or transmitting, or both, an alarm when the mean stimulation frequency exceeds the upper limit value. 